Got a new chain, new chainring, new sprocket on a single speed bike with slidey dropouts. You can get it set up with say 75% of the chain at the right tension but when turned you get an area where the chain then goes really tight, i.e. it’s not even tension when you do a complete revolution. You back off to resolve this bit and then the rest is way too slack. Why the tight spots if it’s all new? Any tips/advice? Cheers

Undo the chain ring bolts – it’s not central on the cranks/around the axle.

You just have to play with chainring position to get it the best you can – there’s usually a few mm of movement available if you play with it.

As long as the chain doesn’t fall off at the slackest point and it’s not too tight at worst you’ll be fine.

Check freewheel/freehub and bottom bracket bearings and the chain join.

Chainset is off centre – see if wwaswas’s tip helps – nothing else will bar a new chainset.

thanks all, will go and have a check

I dicked around trying to centre a chainring using a file. IMO it would have to be seriously off-centred to cause a issue.

Can you derail the chain when it’s in its slackest position?

1.5mm off-centre gives 1.5mm tight and 1.5mm slack = 3mm at dropout – quite a bit.

They usually have a bit of a tight spot where the chainring is not properly round , just set it so it’s not too tight when going over the tight spot and if it runs OK leave it at that . If that doesn’t work send the chainring back .

just slackened chainring bolts, ran the cranks around a few times slowly jiggling the chain in the tight spot and done up again when it felt better. I guess it’s centred better now, amazing a mm or two can make such a difference. Does seem much better now so many thanks for advice

Hard to avoid to some extent unless you have perfectly round and perfectly mounted ring and sprocket.

You back off to resolve this bit and then the rest is way too slack

I have a ~1% worn chain on an oval ring at the moment, you should see how slack that is in places.. as long as it doesn’t come off it’s all ok, the top run will be tight / the lower run loose when you pedal anyway. A SS chain has to get seriously slack to bounce off. ‘Gears chains’ pop off a bit easier, they’re designed to.

avontyrrell – Member
I guess it’s centred better now, amazing a mm or two can make such a difference.

It wouldn’t be nearly as much as a millimetre or two though – ten thou. (0.25mm) can make a big difference in chain tension.